Photo-sensitive electronic components can be used to create electronic imaging systems. These imaging systems can then be employed in a variety of applications. In some applications (e.g., digital photography), creating an image may be the ultimate goal. In other applications, data generated by the imaging system is analyzed for other purposes. As but one illustration, data collected by an imaging array can be used to detect and/or measure motion. Computer pointing or input devices (such as computer mice) are examples of devices that use imaging array data in such a manner.
When designing an imaging array, there is often a trade-off between the photosensing area in each element (or pixel) of the array and the speed with which the array can collect images (or “frames”). At a given illumination intensity, more time is needed to collect sufficient light if the photosensing area is reduced. Conversely, increasing the amount of photosensitive area within array pixels allows faster frame rates. In some applications (e.g., motion-sensing in a computer mouse), the frame rate is quite high (on the order of thousands of frames per second) and light levels may be very low. It is thus beneficial to maximize fill-factor when designing arrays for such applications. Fill-factor (i.e., the ratio within each pixel of light-sensing region to total pixel area) is reduced by elements such as power supply lines and lines carrying signals between the pixels and elements outside the array. The problem becomes more acute as the number of pixels increases. As more and more pixels are added to an array design, there are more and more power and signal lines that must cross over other pixels.